Boost converter circuit is used to boost an input voltage to a higher output voltage. A boost ratio of ten or more is possible, e.g., in portable display applications. A boost converter may be used, e.g., to power a string of white LED diode for LCD backlight. In such situations boost converter may be used to convert a five volt input to an output voltage of up to 50V. A boost converter generally includes five basic components, namely a power semiconductor switch, a diode, an inductor, a capacitor and a modulation controller, such as a pulse width modulation (PWM) controller. There are many different kinds of control systems, pulse width modulation (PWM) is only one of them.
High Voltage and High Power Step-Up, or Boost, Converter are used in many applications such as LCD panel power supplies or LED backlight drivers. A small form factor for the total solution is needed as PCB space is always limited. Reduced PCB area also serves to reduce the manufacturing cost.
FIG. 1 is a circuit diagram of a boost converter integrated circuit (IC) 100 of Prior Art. As shown in FIG. 1, boost converter circuit 100 includes a low voltage integrated circuit (IC) containing a pulse-width modulation (PWM) controller 104 mounted to a first die pad 102, an external sense resistor Rs and an external high voltage NFET 106. An inductor L may be directly coupled between the input voltage VIN of the controller 104 and a drain D of the NFET 106. An external sense resistor Rs may be coupled between a source S of the NFET 106 and ground. An external high voltage (HV) Schottky diode Dsch, and a capacitor C are coupled in series between the drain D and the ground. An output voltage VOUT may be obtained at a point between the Schottky diode Dsch, and the capacitor C. There may be a voltage drop VDIODE across the Schottky diode. The Schottky diode is bonded to a second die pad 108.
Boost converters of the type shown in FIG. 1 having an integrated FET in a small package have been successfully introduced. However, such boost converters use an external discrete Schottky diode. Unfortunately, most integrated Schottky diodes available in commercial IC processes do not have the area efficiency required to meet either the Power (Current) or Voltage requirement. For high power operation, the junction area of the diode must be large so that the diode can carry high current and sustain high voltage.
Co-Packaging of a Schottky diode and an IC has appeared in commercial boost converters intended for LCD backlight. An example of a serial LED driver with a current-regulated, step-up DC/DC converter is a FAN5606, made by Fairchild Semiconductor. This device has a built-in Schottky diode and does not require an external Schottky diode. However, although the Schottky diode may be co-packaged with the IC, such a boost converter requires two die pads, one for the IC and one for the diode, which limits the active area of the components that can be included in a given package. This dictates a larger package form factor. In addition, production costs for such devices tend to be high due to the assembly complexity and the cost of the lead frame for the two die pads.
It is within this context that embodiments of the present invention arise.